There are many occasions when flow in an operating pipeline has to be temporarily plugged, typically in order to repair some component that is partly or wholly inoperative. Similarly, there are occasions when a section of a pipeline under pressure, but not flowing, has to be isolated. Typical situations are when it is desired to close a valve in an operating pipeline and the valve will not close or there is a leaking or inoperative component that has to be replaced. As is well known in the art, many of these situations, such as in chemical plants, refineries and long distance pipelines, require that a bypass be made around the section to be plugged so flow through the pipeline is essentially continuous.
One conventional manner of temporarily plugging a pipeline is to weld a split housing onto the pipeline at a selected location, install a valve and packing element on the split housing and cut a small section of pipe, known as a coupon, out of the pipeline thereby leaving a pair of pipe ends exposed inside the housing. After the cutting device is removed, a pipeline stop is inserted through the valve and packing element and manipulated so it seals against the exposed pipe ends or to a seal inside the split housing thereby stopping flow though the pipeline. After the repairs are conducted on the pipeline, the pipeline stop is removed from the housing and the housing closed up thereby allowing fluids to resume flow through the pipeline.
To these ends, one type of conventional pipeline stop includes a pair of elements having semicylindrical sealing surfaces and a central element that is manipulated to expand the sealing elements. It is this type device to which this invention most nearly relates. Pipeline stops of several types are found in U.S. Pat. Nos. 587,107; 2,655,339; 2,740,606; 3,046,645; 3,155,369; 3,405,739; 3,543,802; 3,833,020; 3,863,667; 4,108,194 and 4,285,368. Another disclosure of interest relative to this invention is found in U.S. Pat. No. 4,405,113.